1. Field of the Invention
The present invention relates to a balancing method of a tunable duplexer usable e.g. in a multimode cellular transceiver. For example, an embodiment of the present invention is applicable to a 3GPP communication system.
2. Related Background Art
Prior art which is related to this technical field can e.g. be found in:    [1] Mikhemar, Darabi, Abidi: “A Multiband RF Antenna Duplexer on CMOS: Design and Performance”, http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=6544685    [2] Abdelhalem, Gudem, Larson: “A tunable differential duplexer in 90 nm CMOS”, http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6242241    [3] US 2011/299436 A1    [4] US 2011/299435 A1    [5] US 2011/300814 A1    [6] US 2011/053539 A1
The following meanings for the abbreviations used in this specification apply:
3GPP third generation partnership project
ADC analog-digital converter
BS base station
CMRR common mode rejection ratio
DSP digital signal processor
DTX discontinuous transmission
FDD frequency division duplexing
IL insertion loss
LNA low noise amplifier
LO local oscillator
LTE long term evolution
PA power amplifier
RF radio frequency
RX receiver
SW software
TDD time division duplexing
TX transmitter
Multimode cellular transceivers cover a large number of frequency bands, and in conventional architectures each band has a separate duplex filter. The duplex filters are expensive and physically large components. Integrated electrical balance duplexers can cover several bands and are thus highly attractive especially for low cost commercial devices.